This invention relates to a tape guide device of a rotary head type video tape recorder for recording and reproducing video signals.
In a rotary head type video tape recorder (VTR) of the helical scanning system, the tape guide device comprises a head cylindrical drum including an upper rotary cylindrical portion and a lower stationary cylindrical portion constituting a stationary cylindrical drum, a shoulder portion formed in the outer circumferential surface of the stationary cylindrical drum and extending over the entire circumference of 360.degree., the shoulder portion having a guide section extending over a part of the entire circumference for guiding a magnetic tape in its travel around the stationary cylindrical drum and a non-guiding section extending over the remaining part of the entire circumference, and a plurality of guide pins each disposed on one of opposite sides of the head cylinder drum for guiding the magnetic tape to and from the head cylindrical drum. The magnetic tape helically contacts the outer circumferential surface of the head cylindrical drum for a circumferential extend on the order of 180.degree. and travels at a predetermined speed while the lower edge of the tape is guided by the guide section which it is in contact. A magnetic head is attached to the upper rotary cylindrical portion and obliquely traverses the magnetic tape as the latter travels around the head cylindrical drum, to record or reproduce video signals on the magnetic tape.
In the prior art, the shoulder portion is formed so as to have a suitable configuration combining straight lines with arcs in the developed circumferential plan view. In the formation of the shoulder portion of the configuration described, difficulties have been experienced in operating the tool rest of a lathe in its machining process, and when operation of the tool rest is not performed properly, the precision with which the shoulder portion is formed is reduced and the circularity of the head cylindrical drum is impaired. The use of such a head cylindrical drum for guiding a magnetic tape results in distorted images reporduced by the VTR because the magnetic tape is not guided accurately.